1. Field of the Invention
This invention relates to organo molybdenum derivatives and their use as multifunctional friction modifier, antiwear, extreme pressure, antioxidant additives for lubricants.
2. Description of Related Art
Regulatory agencies today are seeking to improve the fuel economy of cars on the road through legislation (CAFE requirements) putting this responsibility on the car manufacturers who, in turn, transfer some of this responsibility to the lubricant oil manufacturers via engine oil specifications. It can be seen that as these fuel economy requirements become more stringent, friction modifier additives become more important to incorporate into lubricant compositions. It is an object of this invention to provide a friction modifier additive that imparts a reduction in the coefficient of friction to a lubricant composition.
In addition, zinc dialkyldithiophosphates (ZDDP) have been used in formulated oils as anti-wear and antioxidant additives for more than 50 years. However, zinc dialkyldithiophosphates give rise to ash, which contributes to particulate matter in automotive exhaust emissions. Regulatory agencies are seeking to reduce emissions of zinc into the environment. In addition, the phosphorus is also suspected of limiting the service life of catalytic converters, used on cars to reduce pollution. It is important to limit the particulate matter and pollution formed during engine use for toxicological and environmental reasons, but it is also important to maintain, undiminished, the anti-wear and antioxidant properties of the lubricating oil. In view of the aforementioned shortcomings of the known zinc and phosphorus-containing additives, it is a further object of this invention to provide anti-wear and antioxidant additives that contain neither zinc nor phosphorus.
In developing lubricating oils, there have been many attempts to provide additives that impart anti-frictional or oiliness properties to lubricating oils and molybdenum compounds are known to be useful as friction modifiers, anti-wear, extreme pressure, and antioxidants in lubrication oil compositions.
Thiocarbamate additives for lubricating oils, particularly molybdenum-containing thiocarbamates have been disclosed in the patent literature. For example, U.S. Pat. Nos. 4,395,343; 4,402,840; 4,285,822; 4,265,773; 4,272,387; 4,369,119; 4,259,195; 4,259,194; and 4,283,295, all to DeVries and King, disclose a variety of molybdenum, sulfur, and nitrogen containing compounds, including dithiocarbamates, that are useful as antioxidants for lubricants.
U.S. Pat. No. 3,509,051 discloses various molybdenum dialkyldithiocarbamates, derived from secondary amines, which are said to be useful as antioxidant and antiwear compounds for lubricating oils.
Complexes of molybdenum oxides and nitrogen-containing moieties, including dialkyldithiocarbamates, which are said to have utility as additives for lubricants, are disclosed in U.S. Pat. No. 3,419,589 to Larson et al and U.S. Pat. No. 4,164,473 to Coupland et al.
U.S. Pat. No. 3,541,014 to LeSuer discloses molybdenum complexes of Group II metal-containing compounds, e.g., overbased Group II metal sulfonates that are said to improve extreme pressure properties and antiwear properties in lubricant compositions.
A molybdenum dihydrocarbyldithiocarbamate compound said to be useful as an additive for lubricants is disclosed in U.S. Pat. No. 4,098,705 to Sakurai et al.
U.S. Pat. No. 4,266,945 discloses the preparation of molybdenum-containing compositions by the reaction of an acid of molybdenum or salt thereof, phenol or aldehyde condensation product therewith, and a primary or secondary amine. The preferred amines are diamines such as tallow-substituted trimethylene diamine and their formaldehyde condensation products. An optional but preferred ingredient in the reaction mixture is at least one oil-soluble dispersant. The molybdenum-containing compositions are said to be useful as additives in lubricants and fuels, especially in lubricants when combined with compounds containing active sulfur.
Sulfur and phosphorus-containing molybdenum compositions said to be useful for improving fuel economy for internal combustion engines are disclosed in U.S. Pat. No. 4,289,635 to Schroeck.
U.S. Pat. No. 4,315,826 discloses multipurpose lubricant additives that are prepared by reaction of carbon disulfide with thiomolybdenum derivatives of polyalkenylsuccinimides having basic nitrogen functions. The subject additives function as dispersants and are said to possess excellent anti-frictional properties and to impart anti-wear and anti-oxidant properties to a lubricant.
U.S. Pat. No. 4,474,673 discloses the preparation of anti-friction additives for lubricating oil by reacting a sulfurized organic compound having an active hydrogen or potentially active hydrogen with a molybdenum halide.
U.S. Pat. No. 4,479,883 discloses a lubricating oil composition that contains a relatively low level of phosphorus and is said to have particularly improved friction reducing properties that comprises an ester of a polycarboxylic acid with a glycol or glycerol and a selected metal dithiocarbamate.
U.S. Pat. No. 4,501,678 discloses a lubricant containing molybdenum dialkyldithiocarbamates said to be useful for improving fatigue life of gears.
U.S. Pat. No. 4,765,918 discloses the preparation of a lubricating oil additive by reacting a triglyceride with a basic nitrogen compound to form a reaction product, reacting said reaction product with an acidic molybdenum compound to form an intermediate reaction product, and reacting said intermediate reaction product with a sulfur compound to produce a lubricating oil additive.
U.S. Pat. No. 4,889,647 discloses molybdenum complexes prepared by reacting (a) a fatty oil, (b) diethanolamine, and (c) a molybdenum source. The molybdenum complexes are said to impart antifriction and antiwear properties to lubricating compositions and to decrease fuel consumption in internal combustion engines using them.
U.S. Pat. No. 4,995,996 discloses a lubricating composition comprising a major amount of an oil of lubricating viscosity and a minor amount of an additive having the formula Mo2L4 wherein L is a ligand selected from xanthates and mixtures thereof and, in particular, xanthates having a sufficient number of carbon atoms to render the additive soluble in the oil. In general, the xanthate ligand, L, will have from about 2 to 30 carbon atoms.
U.S. Pat. No. 5,498,809 discloses oil soluble copolymers derived from ethylene and 1-butene that have a number average molecular weight between about 1,500 and 7,500, at least about 30 percent of all polymer chains terminated with ethylvinylidene groups, and ethylene-derived content of not greater than about 50 weight percent, and which form solutions in mineral oil free of polymer aggregates, as determined by light scattering measurements. Lubricating oil additives, particularly dispersants, produced by the functionalization and derivatization of these copolymers are said to have enhanced performance (e.g., improved dispersancy and pour point) in lubricating oil compositions, attributable in part to the combination of properties characterizing the copolymers.
The preparation of nanosized surface-capped inorganic sulfides via intermediate reverse microemulsion formation is described in the following references:
Boakye et al. J. Coll. Interface Sci. 163(1):120-129 (1994) describe the synthesis of molybdenum sulfide nanosized particles in the range of 10-80 nm without surface-capping reagents.
Deng et al., Chem. Lett.(6):483-484 (1997) describe a novel synthetic approach to CdS nanoparticles capped with an electric neutral surface capping agent of 2,2-bipyridine in sodium(bis-2-ethylhexyl) sulfosuccinate (AOT) reverse micelle.
Huang et al., Langmuir 13(2):172-175 (1997) describe copper nanoparticles capped with poly-(N-vinylpyrrolidone) and prepared by the reduction of Copper II acetate in water and 2-ethoxyethanol using hydrazine under reflux.
Meldrum et al. J. Chem. Soc. Faraday Trans. 91 (4):673-680 (1995) describe the formation of thin particulate films from silver nanoparticles, generated by the sodium borohydride reduction of aqueous silver nitrate within sodium(bis-2-ethylhexyl) sulfosuccinate reverse micelles in 2,2,4-trimethylpentane and capped with octadecanethiol.
Motte et al., J. Phys III 7(3):517-527 (1997) describe reverse micelles that have been used to synthesize 5.6 nm silver sulfide particles. These nanoparticles are coated with dodecanethiol, extracted from reverse micelles, and then dissolved in heptane.
Motte et al., J. Phys. Chem., 99(44):16425-16429 (1995) describe utilization of dodecanethiol for surface capping of various metal sulfide nanosized particles.
Pileni et al. Surf. Rev. Letters 3(1):1215-1218 (1996) describe synthesis of silver sulfide semiconductor clusters encapped with dodecanethiol.
Steigerwald et al. J. Amer. Chem. Soc. 110(10):3046-3050 (1988) describe a synthesis of nanometer-sized clusters of CdSe using organometallic reagents in inverse micellar solution and chemical modification of the surface of these cluster compounds to form a PhSe layer on the CdSe surface.
Yanagida et al. Bull. Chem. Soc. Jpn. 68(3):752-758 (1995) describe size-controlling CdS nanocrystallites that were prepared by using thiophenol or hexanethiol as a capping reagent by controlling the ratio of Cd++ to bis(trimethylsilyl) sulfide as a source of the sulfide ion in reversed micelles.
Unfortunately, a problem remains in that many molybdenum compounds exhibit poor solubility in lubricant oils. No disclosures are known to the present inventors that teach or even suggest nanosize particles comprising a molybdenum/sulfur moiety whose surface is modified with an appropriate ligand that prevents the coagulation of the nanoparticles and provides their solubility and stability in hydrocarbons or similar solvents, which further improves anti-wear properties, antioxidant properties, extreme pressure properties, and friction modifying properties in lubricating oil compositions.